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Math & Trig
The Excel LN function returns the natural logarithm of a number — the logarithm to base e (≈ 2.71828). It is the exact inverse of EXP.
Quick answer:
=LN(EXP(1)) ln(e) = 1
Syntax
=LN(number)
| Argument | Description | |
|---|---|---|
number | Required | The positive real number whose natural logarithm you want. Must be greater than zero. |
How to use it
LN answers “e to what power gives this number?” — the logarithm to base e:
=LN(EXP(1)) // ln(e) = 1
=LN(1) // ln(1) = 0
=LN(10) // ~2.302585
For a different base, use LOG(number, base); for base 10 specifically, LOG10. LN and EXP are inverses: =EXP(LN(5)) = 5.
Positive numbers only. The natural log is undefined for zero or negative values, so =LN(0) and =LN(-2) both return a #NUM! error.
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Result:
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Frequently asked questions
What base does LN use?
Base e (about 2.71828), the natural logarithm. For base 10 use LOG10, and for any other base use
LOG(number, base).Is LN the inverse of EXP?
Yes.
=LN(EXP(1)) = 1 and =EXP(LN(5)) = 5. LN reverses what EXP does.Why does LN of zero or a negative number error?
The natural log is only defined for positive numbers, so
=LN(0) and =LN(-2) return a #NUM! error.What is the difference between LN and LOG?
LN is fixed to base e. LOG defaults to base 10 but accepts a second argument for any base, so
=LOG(100) = 2 and =LOG(8,2) = 3.Master functions like this in one day
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